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The direst projected effects of the climate emergency for the UK have been mapped by scientists, including a searing 4C rise in average temperatures to a two-metre increase in ocean levels. A separate possibility foresees a decline of 6C in temperatures following the collapse of critical Atlantic Ocean currents, which would severely impact farming and power requirements.

Credible Events, Not Forecasts

These consequences, a number of which are associated with irreversible climate shifts, are seen as unlikely but credible. The scientists said that these models addressed a shortfall in risk assessment that had rendered the UK not ready for extreme outcomes.

"The climate extremes we have outlined should not be seen as certainties, but they are possible," said the lead researcher who oversaw the research. "The nation has been planning lacking the methods to assess catastrophic outcomes. We've now supplied decision-makers what they need to prepare for future conditions they pray never occur, but must not overlook."

A Range of Extreme Weather Possibilities

A further series of dire projections maps the potential extent of harsh climate between now and the end of the century. These suggest that temperatures could skyrocket in certain periods by up to 6C above historical levels, while rainfall could be 300% of normal levels.

The likelihood of the catastrophic events occurring remains uncertain due to unknown factors about what action will be implemented to combat global warming and how the climate system will respond. This approach was likened to national security risk assessments or scenario planning for financial systems.

Major Outcome Details

• Four-Degree Warming: Global temperatures exceeding 4C by 2100 could occur if climate action breaks down or if strong feedback loops including the Amazon basin dying release its huge repository of carbon. This would result in severe and lengthy heatwaves and droughts affecting the UK in summer.
• AMOC Shutdown: A key circulation system, the AMOC, is losing strength and losing stability due to ocean warming. A collapse beginning in 2030 would lead to a six-degree temperature drop in the UK. "Farming would struggle enormously and water supplies would be fundamentally reshaped," said Arnell.
• Rapid Sea Level Rise: A rise of 2.0-2.2 metres around the UK by 2100 could occur if ice sheets in the Arctic and Antarctic disintegrate quickly, submerging seaside communities. In contrast to the other scenarios, this risk is already recognized by coastal engineers.
• Clean Air Warming: Temperatures could also be pushed higher by about 0.75C if industrial aerosols is sharply cut. This counterintuitive effect occurs because tiny specks from fossil fuel combustion block sunlight from reaching the ground.

Preparing for the Extreme

These dire projections could be used to inform the construction of long-term infrastructure, for example housing developments, nuclear power stations and urban drainage systems. Awareness of these climate risks could also speed the transition to slash fossil fuel emissions.

The research formulated the severe projections using a combination of past data and records, digital projections and established principles. These outcomes exclude broader worldwide issues such as the global food shortages and increased conflict.

The research was initiated as part of a national climate resilience programme. Independent analyses have cautioned that insufficient focus was being given to catastrophic yet improbable risks.

The government's climate advisors has said that the UK must "prepare for two degrees of warming" and assess the risks for 4C. Past policy documents have been criticised as being "very weak" by environmental groups.

An official statement said: "Climate change is at the core of this government’s agenda, both building resilience and transitioning to a low-carbon economy. It is essential that the UK is resilient for the effects."